Synthesis of mono-phosphido, mono-dppm bridged Pd(I) cationic dimers. Structure and fluxionality of [Pd2( μ-PtBu2) ( μ-dppm)( η1-dppm) 2]CF3SO3 (dppm = bis-diphenylphosphinomethane)

Article abstract of DOI:10.1016/0022-328X(95)06019-S

The dimer [Pd₂( μ-P^tBu₂)( μ-P^tBu₂H)(P^tBu₂H)₂]⁺X^- [(1)⁺BF₄^-, X = BF₄; (1)⁺Tf^-, X = CF₃SO₃], with two terminal and one bridging weakly bonded di-tert-butylphosphine molecules, proved to be an excellent reagent for the preparation of new mono-phosphido, mono-dppm bridged palladium(I) derivatives of general formula [Pd₂( μ-P^tBu₂)( μ-dppm)(PR₃)₂]⁺X^- [(2)⁺X^-, PR₃ = P^tBu₂H; (3)⁺X^-, PR₃ = PMe₃; (4)⁺X^-, PR₃ = PEt₃; (5)⁺X^-, PR₃ = η¹-dppm]. The cation (5)⁺ has one dppm molecule terminally bonded to each palladium atom in a monodentate fashion. As demonstrated by solution ³¹P{¹H} NMR spectra, the two phosphorus atoms of each η¹-dppm molecule are rapidly scrambled without dissociation through an intermediate chelate coordination of the disphosphine molecule. The same fluxional behavior was observed in the neutral [Pd₂( μ-P^tBu₂)( μ-dppm)(SPh)(η¹ - dppm)] (6) obtained by reaction of (5)⁺BF₄^- with PhSNa. The solid state structures of complexes (3)⁺Tf^- and (5)⁺Tf^- were determined by X-ray diffraction methods.